OPEC members appear to be complying with agreed production cuts, but Saudi Arabia is overcompensating for some of its fellow oil producers.
The OPEC deal, agreed late last year, requires 10 member states to reduce their collective output by 1.2 million barrels per day (bpd) starting from January 1.
S&P Global Platts, which monitors monthly OPEC production, released its latest survey earlier this week and found members achieved 91 percent of their required cuts for the month of January, or 1.14 million bpd.
"OPEC spent much of the last half of last year talking up this deal. We wanted to see whether they were actually going to walk the walk and not just talk the talk," Herman Wang, OPEC specialist at S&P Global Platts, told CNBC.
"The 10 members that were required to cut production under this deal have achieved 91 percent, 1.14 million bpd, of cutting from October levels, which was where this deal was benchmarked from."
However, the compliance rate has not been spread evenly. Some countries, specifically Saudi Arabia, Kuwait and Angola, are over complying which is compensating OPEC members who are under complying.
For instance, Saudi Arabia produced 9.98 million bpd in January, well below its allocation of 10.06 million bpd.
Other counties, such as Algeria, Venezuela and Iraq, are producing more oil than their quota. Iraq in particular was singled out by the S&P Global Platts report, as its January output of 4.48 million bpd was well above its quota of 4.35 million bpd (although the report noted Iraq's output had declined 150,000 bpd from December).
"Saudi Arabia is bearing the brunt of these cuts," said Wang.
"They are going above and beyond, compensating a little bit for some of their cohorts within OPEC that are not quite in full compliance. Now how long Saudi Arabia is willing to shoulder the burden of these cuts if it proves some of their cohorts are not fully complying with the deal remains to be seen."